but(FormFiled): Floating label hide/show not responsive when set to outline appearance.

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

When you have a mat form field and the mat-label is conditional. If the view starts with the label and gets remove with @if in template it is perfectly fine. Will disappear and reappear. If the view starts with-out the mat label rendered, the label will get rendered but the component, 'MatFormFieldNotchedOutline" still has the class, 'mdc-notched-outline--no-label', so the display is set to none.

Looks as though if the mat-label is not there on view init it is not responsive.

The behavior works fine with fill appearance.

### Reproduction

StackBlitz link:
Steps to reproduce:
1.
2.

### Expected Behavior

When mat-label gets rendered in even after init, i.e. Using a structural directive or decorator such *ngIf or @if. The label should show no matter the appearance.

### Actual Behavior

When you have the appearance set to outline and the view is initially rendered without the label it is not responsive and will not show up.

### Environment

- Angular: 18.2.10
- CDK/Material: 18.2.10
- Browser(s): Edge, Chrom
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

从 MatFormFieldNotchedOutline 针对 outline 外观的行为开始，并复现初始化后使用 @if 条件渲染的 mat-label。当 outline 不再保留无 label 状态，并且在添加 label 时显示该 label，与现有的 fill 行为一致时，即表示完成。

由索引模型根据 Issue 内容生成。